1. Field of the Invention
The present invention relates generally to a semiconductor light emitting device and a method for manufacturing the same.
2. Related Background Art
In recent years, semiconductor white light emitting devices are widely noticed as successors to incandescent lamps and fluorescent lamps. Such a semiconductor white light emitting device is characterized by a simple driving circuit and small electric power consumption.
As the semiconductor white light emitting devices, there are proposed devices using GaN compound semiconductor light emitting elements (GaN compound semiconductor white light emitting devices) and devices using ZnSe compound semiconductor light emitting elements (ZnSe compound semiconductor light emitting devices).
The GaN compound semiconductor white light emitting devices are described in, e.g., Japanese Patent Laid-Open Nos. 10-242513, 10-12916 and 11-121806.
The GaN compound semiconductor white light emitting device disclosed in Japanese Patent Laid-Open No. 10-242513 comprises a GaN compound semiconductor light emitting element for emitting blue light, and a YAG:Ce fluorescent material for absorbing the emitted blue light to emit yellow light, to achieve white light by mixing the blue light emission and the yellow light emission. The YAG:Ce fluorescent material is mixed in a resin to be applied to a portion surrounding the semiconductor light emitting element.
The GaN compound semiconductor white light emitting device disclosed in Japanese Patent Laid-Open No. 10-12916 comprises a GaN compound semiconductor light emitting element for emitting ultraviolet light, and three kinds of fluorescent materials for absorbing the emitted ultraviolet light to emit red light, the green light and the blue light, to achieve white light by mixing red light emission, green light emission and blue light emission. The fluorescent materials are mixed in a resin to be applied to a portion surrounding the semiconductor light emitting element.
The GaN compound semiconductor white light emitting device disclosed in Japanese Patent Laid-Open No. 11-121806 comprises three kinds of active layers including an active layer for emitting red light, an active layer for emitting green light and an active layer for emitting blue light, to achieve white light by mixing the red light emission, the green light emission and the blue light emission. The three kinds of active layers are separately provided, and a current is injected into each of the active layers.
A ZnSe compound semiconductor light emitting device comprises a ZnSe compound semiconductor light emitting element for emitting blue light, and an emission center, formed on the substrate, for emitting yellow light, to achieve white light by mixing the blue light emission and the yellow light emission.
However, as a result of the inventors"" experimental manufacture and evaluation, it was found that, in the conventional semiconductor white light emitting devices, there are problems in that the tone of white light varies for each device and that the tone deteriorates with age, as follows.
First, when a fluorescent material is mixed in a resin to be applied to a portion surrounding a semiconductor element as in the semiconductor white light emitting device disclosed in Japanese Patent Laid-Open No. 10-242513, it is difficult to maintain the quantity of the fluorescent material for each element at a constant level, so that the quantity of the fluorescent material varies for each device. For example, when the quantity of the fluorescent material is large, the intensity of emitted yellow light is high, so that the tone of white light is close to yellow. On the other hand, when the quantity of the fluorescent material is small, the intensity of emitted yellow light is low, so that the tone of white light is close to blue. For that reason, the tone of white light varies for each device. In addition, since the fluorescent material is deteriorates more easily than the semiconductor light emitting element, the tone greatly deteriorates with age. For example, when the fluorescent material deteriorates to and the yellow light emission weakens the tone is close to blue.
In addition, when three kinds of fluorescent materials are used as in the semiconductor white light emitting device disclosed in Japanese Patent Laid-Open No. 10-12916, it is difficult to carry out a proper mixing of the fluorescent materials, so that the compounding ratio of the fluorescent materials varies for each device. For example, when the quantity of the blue light emitting fluorescent material is large, the tone is close to blue. For that reason, the tone of white light varies every device. Also, as in the case of the above described devices, the variation in tone due to the variation in quantity of the fluorescent materials, and the variation in tone due to the deterioration of the fluorescent materials are easily caused.
In addition, in the structure wherein three kinds of active layers for red light emission, green light emission and blue light emission are used as in the semiconductor white light emitting device disclosed in Japanese Patent Laid-Open No. 11-121806 the light emission of each layer varies in accordance with the injected current, so that it is difficult to adjust the balance of light emissions of three colors. For example, when the current injected into the blue light emitting active layer is too large, the tone of white light is close to blue. For that reason, the tone of white light varies.
Moreover, in the structure wherein an emission center is formed on the substrate as in the ZnSe compound semiconductor light emitting device, it is difficult to maintain the quantity of the emission center at a constant level for each wafer, so that the quantity of the emission center varies for each wafer. For example, when the quantity of the emission center is large, the quantity of emitted yellow light is large, so that the tone of white light is close to yellow. On the other hand, when the quantity of the emission center is small, the quantity of emitted yellow light is small, so that the tone is close to blue. For that reason, the tone of white light varies.
Thus, it was found that, in the conventional semiconductor white light emitting devices, there are problems in that the tone of white light varies for each device and that the tone deteriorates with age.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a semiconductor light emitting device wherein the variation in tone is small and the deterioration of tone is slow.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, there is provided a semiconductor light emitting device comprising: a semiconductor light emitting element which has an active layer for emitting primary light having a first wavelength by current injection; and at least one semiconductor laminate which is bonded to said semiconductor light emitting element and which has a light emitting layer, excited by said primary light, for emitting secondary light having a second wavelength different from said first wavelength, wherein said primary light and said secondary light are mixed to be outputted.
The active layer may be a InpGaqAl1-p-qN (0xe2x89xa6pxe2x89xa61, 0xe2x89xa6qxe2x89xa61, 0xe2x89xa6p+qxe2x89xa61) active layer. And the InpGaqAl1-p-qN active layer includes, for example, an active layer having a multi-quantum well structure of InGaN and GaN. The light emitting layer may be an InbGacAl1-b-cP (0xe2x89xa6bxe2x89xa61, 0xe2x89xa6cxe2x89xa61, 0xe2x89xa6b+cxe2x89xa61) light emitting layer.
According to another aspect of the present invention, there is provided a semiconductor light emitting device comprising: A semiconductor light emitting device comprises: a GaAs substrate; an InbGacAl1-b-cP (0xe2x89xa6bxe2x89xa61, 0xe2x89xa6cxe2x89xa61, 0xe2x89xa6b+cxe2x89xa61) light emitting layer which is formed on said GaAs substrate and which is excited by primary light having a first wavelength for emitting secondary light having a second wavelength; a buffer layer formed on said InbGacAl1-b-cP light emitting layer; and a ZnjCd1-jSe (0xe2x89xa6jxe2x89xa61) active layer which is formed on said buffer layer and which emits said primary light having the first wavelength by current injection; wherein said primary light and said secondary light are mixed to be outputted.
The ZnjCd1-j Se active layer includes, for example, an active layer having a multi-quantum well structure of ZnCdSe and ZnSe.
According to another aspect of the present invention, there is provided a method for manufacturing a semiconductor light emitting device, the method comprising: a semiconductor light emitting element forming step including a step of forming on a first substrate a semiconductor layers, which has an active layer for emitting primary light having a first wavelength by current injection; a semiconductor laminate forming step including a step of forming on a second substrate a semiconductor layers, which includes a light emitting layer excited by said primary light for emitting secondary light having a second wavelength different from said first wavelength; and a bonding step including a step of integrally bonding said semiconductor light emitting element to said semiconductor laminate.
According to another aspect of the present invention, there is provided a method for manufacturing a semiconductor light emitting device, the method comprising the steps of: forming on a GaAs substrate an InbGacAl1-b-cP (0xe2x89xa6bxe2x89xa61, 0xe2x89xa6cxe2x89xa61, 0xe2x89xa6b+cxe2x89xa61) light emitting layer, which is excited by blue light for emitting yellow light; forming a buffer layer on said InbGacAl1-b-cP light emitting layer; and forming on said buffer layer a ZnCe compound active layer, which emits said blue light by current injection.
According to a further aspect of the present invention, there is provided a semiconductor light emitting device comprising: a substrate; a buffer layer formed on said substrate; a first conductive type InrGasAl1-r-sN (0xe2x89xa6rxe2x89xa61, 0xe2x89xa6sxe2x89xa61, 0xe2x89xa6r+sxe2x89xa61) cladding layer formed on said buffer layer, an InpGaqAl1-p-qN (0xe2x89xa6pxe2x89xa61, 0xe2x89xa6qxe2x89xa61, 0xe2x89xa6p+qxe2x89xa61) active layer formed on said first conductive type InrGasAl1-r-sN cladding layer and provided with an ion implantation region into which ions selected from the group consisting of fluorine, oxygen, nitrogen, carbon and sulfur have been injected, regions other than said ion implantation region emitting primary light having a first wavelength, and said ion implantation region emitting secondary light having a second wavelength different from said first wavelength; and a second conductive type IntGauAl1-t-uN (0xe2x89xa6txe2x89xa61, 0xe2x89xa6uxe2x89xa61, 0xe2x89xa6t+uxe2x89xa61) cladding layer formed on said active layer.
According to a still further aspect of the present invention, there is provided a semiconductor light emitting device comprising: a semiconductor light emitting element which has an active layer for emitting primary light having a first wavelength by current injection; reflector for reflecting said primary light emitted from said semiconductor light emitting element; and fluorescent material which is applied on part of said reflector and which is excited by said primary light for emitting secondary light having a second wavelength different form said first wavelength.